1. Field of the Invention
The present invention relates to ratchet assemblies for positioning disc-like film units in a photographic printer.
2. Description of the Prior Art
Apparatus for holding and indexing conventional strip film on a photographic printer so that selected image frames are positioned at a print gate for transfer of the image to photographic print paper are well known in the art. However, this type of apparatus is wholly unsuited for positioning selected image frames of a disc-like film unit at a print gate wherein the individual image frames are located circumferentially about a central hub. Examples of a disc film unit are disclosed in the following U.S. patents:
______________________________________ Inventor U.S. Pat. No. ______________________________________ Sethi 4,194,822 Morse 4,208,116 Harvey et al 4,208,117 Sethi et al 4,212,673 Harvey et al 4,255,034 Harvey 4,264,169 Harvey et al 4,268,145 ______________________________________
A print gate indexing device for a disc-like film unit is disclosed in Research Disclosure of August, 1978, Disclosure No. 17287. Using the print gate indexing device, each image frame is manually advanced into the print gate. The disc-like film unit is held in a single horizontal plane while selected image frames are rotationally indexed to the print gate. However, the manner of indexing individual film frames is unsuitable for semi-automatic or automatic photographic printers.
A rotational positioning device is also disclosed in Research Disclosure of August, 1978, Disclosure No. 17289. The rotational positioning device includes an assembly from which a central shaft extends upwardly for coaxially centering the disc-like film unit on the assembly. A pair of pins also extend upward from the assembly for extending through cooperating apertures in the hub of the disc film unit. No apparatus for indexing the individual film frames is shown.
The Clifton et al U.S. Pat. No. 4,203,664 illustrates a ratchet assembly used to position a disc film unit. A pneumatically operated drive pawl is provided for driving a ratchet gear. However, such a ratchet assembly does not ensure optical centering of each individual film unit indexed to the print gate aperture since the problem of individual film frame being indexed with the ratchet assembly past the optical center is present.
The Modney et al U.S. Pat. No. 4,202,733 shows a wheel beneath the disc film unit holder having a plurality of notches corresponding to the number of frames in a disc film unit. A pair of diametrically opposed blocks containing ball plungers engage an opposed pair of diametrically opposed notches in the wheel when the balls and notches are aligned. The wheel is allowed to rotate, thereby indexing individual film frames, when the balls are withdrawn from the notches, the wheel rotates freely. The apparatus disclosed in the Modney et al patent is, however, rather complicated and does not ensure automatic optical centering of each individual film frame upon indexing.